1. Field of the Invention
The present invention relates generally to processing and amplification of optical signals, and particularly, to a novel pulse amplification apparatus and method of operation that provides enhanced optical signal gain at reduced cost and complexity.
2. Description of the Prior Art
Optical pulses have found wide applications in, for example, telecommunication, medical equipments/devices, testing and measurement equipments, food/agricultural industries, and even military/weaponry applications. Among key properties of a series of optical pulses are the duration of the pulses, peak intensity, and repetition rate. Other properties may include rise/fall time of the pulse shape and wavelength of the light. Normally, a series of optical pulses generated by a laser diode (LD), or a light-emitting diode (LED), may not have the intensity sufficient for most of the applications such as, for example, medical devices. Therefore, the intensity of optical pulses may need to be boosted, or amplified, to reach a certain required peak power level. For example, FIG. 1 depicts a prior art optical pulse amplifier apparatus 10 that includes amplifier device 15 for amplifying laser diode generated optical pulses 12, labeled P1, . . . , P4, with fixed pulse width at predetermined time interval t-1, . . . , t4, respectively. In this example, the amplifier device may be characterized by a gain (G) of, e.g., about 10 dB to 15 dB. With an input pulse of peak power about −10 dBm to −15 dBm, by applying this prior art apparatus 10, an output pulse may be obtained having a peak power ranging from about −5 dBm to about +5 dBm. It is apparent that, for some applications, this apparatus 10 may not provide optical pulses with sufficient peak power.
In a further prior art apparatus 20, depicted in FIG. 2A, a series of optical signal amplifiers 15a, 15b, 15c, for example, are cascaded to provide larger amplification/gain to the optical pulses 12, labeled P1, . . . , P4, as in FIG. 1. In this example, the output pulse peak power, which may be estimated as P′n=G3*Pn, may achieve an output pulse peak power level higher than that by using prior art apparatus 10. In the above equation, Pn denotes peak power of input pulse n, P′n denotes peak power of amplified output, and G denotes gain of each optical signal amplifier 15a, 15b, and 15c (assuming all three amplifiers have the same gain). However, such an apparatus 20 has drawbacks which may include, for example, the high cost associated with using multiple amplifiers and an early point of saturation, e.g., at +11 dBm output, such as shown in FIG. 2B, although some un-proportionally expensive amplifiers may provide a higher saturated output power.
Therefore, it would be highly desirable to provide a novel optical pulse amplification apparatus that enhances amplification of a series of optical pulse signals so as to achieve certain required peak power levels.